Considerable risk is encountered when technology is scaled up from pilot plant scale to commercial plant scale in order to reap the benefits of economy of scale. Fluid bed reactors, such as three-phase slurry reactors and two-phase fluidised bed reactors, typically exhibit scale-dependent macro-mixing effects and the aforementioned risk is thus applicable when fluid bed reactors are scaled up. It will thus be an advantage if a method can be found which can significantly reduce the risk associated with upscaling of fluid bed reactors. In addition, reactor designs in which the mixing patterns inside the reactor can be more readily modelled or predicted from experimentation have the benefit that the extent of usually undesirable back-mixing can be limited thereby potentially allowing an optimal combination of desirable plug-flow characteristics (usually good productivity and good selectivity) and well-mixed characteristics (often required for desirable solids distribution and even temperature profiles).
The applicant is aware of U.S. Pat. No. 6,375,921, WO 99/00191, FR 1603546, U.S. Pat. No. 2,853,369 and GB 728543. U.S. Pat. No. 6,375,921 discloses a three-phase slurry vessel with perforated trays with a substantially uniform distribution of holes, which can be used for counter-current operation. WO 99/00191 is concerned with methods for in-situ regeneration of partially and reversibly deactivated catalysts used in bubble column reactors. This document proposes providing a reactor shell in which is placed a draft tube located coaxially within the reactor shell. FR 1603546 deals with problems associated with growing yeast on an industrial scale, more particularly with problems regarding ensuring good contact of the yeast with oxidising gas and two immiscible liquid phases. FR 1603546 proposes a reactor defining a flow path having intercalated concentrically arranged upflow and downflow channels. U.S. Pat. No. 2,853,369 attempts to address the problem of back-mixing by sub-dividing a reactor into a plurality of channels. GB 728543 is concerned with improving hydrocarbon synthesis in a slurry reactor. This document teaches the use of a tower-like reactor with cooling being performed in a number of vertically spaced stages in the reactor. None of these documents deals specifically with ways to reduce the risk encountered when technology is scaled up from pilot plant scale to commercial plant scale, or proposes reactor designs in which the mixing patterns inside the reactor can be more readily modelled or predicted from experimentation.